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Chapter 25: Problem 11

Define natural selection and fitness.

Short Answer

Expert verified
Natural selection is the process where organisms better adapted to their environment survive and reproduce. Fitness measures an organism's success in passing genes to the next generation.

Step by step solution

01

Understanding Natural Selection

Natural selection is a process in biology where organisms with traits that are favorable for their environment are more likely to survive and reproduce. This process leads to the gradual adaptation of species over time, as advantageous traits become more common in the population through successive generations.
02

Explaining Fitness

In the context of evolution, fitness refers to the ability of an organism to survive and reproduce in its environment. It's a measure of how well a particular genotype or phenotype can pass on its genes to the next generation, thereby contributing to the evolutionary process.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Fitness
In the realm of biology, fitness is not about how fast you can run or how strong you are in a physical sense. Instead, it reflects an organism's ability to survive and reproduce in its particular environment.
  • Fitness is crucial because it determines which traits become more common in a population over generations.
  • Organisms with higher fitness levels are more likely to pass on their genes to their offspring.
  • Fitness can vary within the same species, depending on environmental factors.
If a genotype has traits that increase an organism's longevity and reproductive success, that genotype is considered to have high fitness. This doesn鈥檛 always mean the most aggressive or the biggest organism but often, the best adapted to the current environment. This dynamic is what powers the engine of evolution.
Evolution
Evolution is the process by which species of organisms change over time through variations in their genetic material. These changes are driven by mechanisms like natural selection, mutation, and genetic drift. Evolution can be understood through several key elements:
  • Inheritance: Genetic information is passed from generation to generation.
  • Variation: Individuals within a population may have different genetic traits.
  • Selection: Some traits provide a survival and reproductive advantage.
Over many generations, the accumulation of these changes can lead to the emergence of new species. This process of evolution is not directed or intentional but is a natural consequence of varying fitness levels among individuals in a population.
Adaptation
Adaptation is a central concept in understanding how organisms become better suited to their environment. It occurs when a trait enhances an individual's fitness in its current environment, becoming more common in the population over time. Adaptations can appear in different forms:
  • Structural adaptations are physical features of an organism, like the long neck of a giraffe, which helps it reach leaves higher in trees.
  • Behavioral adaptations include activities that help an organism survive, like how birds migrate to avoid harsh winters.
  • Physiological adaptations involve internal functions, like how some fish can regulate their internal salt concentrations to live in salty waters.
Through these adaptations, species can thrive in otherwise challenging environments, demonstrating the power of natural selection in shaping the biological world.
Genotype
The genotype is the genetic makeup of an organism, consisting of all the genes present in its DNA. Each individual inherits genes from its parents, which dictate its specific traits.
  • Genotypes are often denoted by using letters, with capital letters representing dominant alleles and lowercase for recessive alleles.
  • While the genotype sets the groundwork, it is the interaction with the environment that will ultimately determine how these traits manifest.
For example, an organism might have a genotype that codes for blue eyes, but if environmental factors modify the development process, the phenotype (or visible trait) might differ. In the grand scheme of evolution, genotypes that result in higher fitness levels are more likely to be preserved and passed on to subsequent generations.
Phenotype
The phenotype of an organism is the set of observable traits, such as its morphology, development, biochemical or physiological properties, and behavior. The phenotype results from the expression of an organism's genotype in conjunction with environmental influences.
  • Traits such as eye color, height, and petal color in flowers are examples of phenotypes.
  • Phenotypes are what natural selection acts upon, as these traits will determine the individual's success in survival and reproduction.
Two organisms with the same genotype might exhibit different phenotypes if raised in different environments. For example, identical twins may have different skin tones due to differences in sun exposure. Understanding the difference between genotype and phenotype is crucial in fields like genetics and evolutionary biology, as it helps explain how organisms adapt and evolve over time.

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Most popular questions from this chapter

In a large, randomly mating population, the frequency of an autosomal recessive lethal allele is \(0.20 .\) What will the frequency of this allele be in the next generation if all homozygotes die before reproducing?

Compare and contrast the effects of mutation, migration, genetic drift, and natural selection on genetic variation within populations and on genetic divergence between populations.

In German cockroaches, curved wing ( \(c v\) ) is recessive to normal wing \(\left(c v^{+}\right) .\) Bill, who is raising cockroaches in his dorm room, finds that the frequency of the gene for curved wings in his cockroach population is \(0.6 .\) In his friend Joe's apartment, the frequency of the gene for curved wings is 0.2. One day Joe visits Bill in his dorm room, and several cockroaches jump out of Joe's hair and join the population in Bill's room. Bill estimates that, now, \(10 \%\) of the cockroaches in his dorm room are individual roaches that jumped out of Joe's hair. What is the new frequency of curved wings among cockroaches in Bill's room?

In a large, randomly mating population, the frequency of the allele (s) for sickle-cell hemoglobin is \(0.028 .\) The results of studies have shown that people with the following genotypes at the beta-chain locus produce the following average numbers of offspring: $$\begin{array}{cc} \text { Genotype } & \text { Average number of offspring } \\ \text {} & \text { offspring produced } \\ \text { SS } & 5 \\ \text { Ss } & 6 \\ \text { ss } & 0 \\ \end{array}$$ a. What will the frequency of the sickle-cell allele (s) be in the next generation? b. What will the frequency of the sickle-cell allele be at equilibrium?

What factors affect the rate of change in allelic frequency due to natural selection?
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